1. Field of the Invention
The present invention relates to novel synthetic processes for preparing complexes and, more particularly, to novel synthetic processes for preparing luminescent iridium complexes and precursors thereof.
2. Description of Related Art
In addition to inorganic light emitting diodes (LEDs), organic light emitting diodes (OLEDs) made of organic materials have attracted a great deal of attention for lightening and display applications, and have been applied in many products, such as mobile phones, liquid crystal displays, flexible displays etc., owing to their low cost, reduced weight, compact volume, low operating voltage and flexibility.
Like conventional inorganic light emitting diodes (LEDs), electrons and holes, formed in OLEDs under electric fields generated by applying voltage, will move towards the cathode and the anode, respectively, and then recombine in an organic layer to form excitons capable of radiatively relaxing from their excited state to the ground state.
The wavelength of light emitted from OLEDs depends on energy gap between HOMO and LUMO of emissive organic materials applied in OLEDs. Compounds capable of emitting phosphorescent light include transition metal complexes, such as osmium complexes, iridium complexes, platinum complexes, ruthenium complexes, rhodium complexes etc., which exhibit enhanced luminescence efficiency and have reduced half-life period of phosphorescence.
Among these transition metal complexes, iridium complexes can show high phosphorescence emission at room temperature, and the tris-cyclometalated iridium complex, fac-[Ir(ppy)3], is one of the best green phosphorescent materials and can be used as a phosphorescent dopant in an emissive layer of an OLED. Tamayo et al. (Tamayo et al., 2003) published synthesis of fac-[Ir(ppy)3], in which fac-[Ir(ppy)3] was synthesized by reacting [Ir(acac)3] with 2-phenylpyridine (Hppy) (about 3-3.5 equivalents) in an organic solvent by heating under reflux of glycerol. After using a silica-gel chromatographic column, fac-[Ir(ppy)3] can be obtained in a yield of 45-60%. In addition, mer-[Ir(ppy)3] displays similar luminescent behavior to that of fac-[Ir(ppy)3] and can also be used as a phosphorescent dopant in an emissive layer of an OLED. Tamayo et al. (Tamayo et al., 2003) published synthesis of mer-[Ir(ppy)3], in which mer-[Ir(ppy)3] was synthesized by reacting [Ir2(ppy)4Cl2] with K2CO3 (5-10 equivalents) and 2-phenylpyridine (Hppy) (about 2-2.5 equivalents) in an organic solvent by heating under reflux of glycerol. After using a silica-gel chromatographic column, mer-[Ir(ppy))] can be obtained in a yield of 68-80%.
Therefore, it is desirable to provide easily operated synthetic processes for preparing luminescent iridium complexes, fac-[Ir(ppy)3] and mer-[Ir(ppy)3], in a satisfactory yield better than 85% without using a chromatographic column for purification.